drm/i915/guc: Fix error capture for virtual engines

GuC based register dumps in error capture logs were basically broken
for virtual engines. This can be seen in igt@gem_exec_balancer@hang:
  [IGT] gem_exec_balancer: starting subtest hang
  [drm] GPU HANG: ecode 12:4:e1524110, in gem_exec_balanc [6388]
  [drm] GT0: GUC: No register capture node found for 0x1005 / 0xFEDC311D
  [drm] GPU HANG: ecode 12:4:00000000, in gem_exec_balanc [6388]
  [IGT] gem_exec_balancer: exiting, ret=0

The test causes a hang on both engines of a virtual engine context.
The engine instance zero hang gets a valid error capture but the
non-instance-zero hang does not.

Fix that by scanning through the list of pending register captures
when a hang notification for a virtual engine is received. That way,
the hang can be assigned to the correct physical engine prior to
starting the error capture process. So later on, when the error capture
handler tries to find the engine register list, it looks for one on
the correct engine.

Also, sneak in a missing blank line before a comment in the node
search code.

v2: Fix null pointer deref on non-GuC platforms.
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230428185636.457407-5-John.C.Harrison@Intel.com

drivers/gpu/drm/i915/gt/uc/intel_guc_capture.c

@@ -1540,6 +1540,36 @@ void intel_guc_capture_free_node(struct intel_engine_coredump *ee)
 	ee->guc_capture_node = NULL;
 }
 
+bool intel_guc_capture_is_matching_engine(struct intel_gt *gt,
+					  struct intel_context *ce,
+					  struct intel_engine_cs *engine)
+{
+	struct __guc_capture_parsed_output *n;
+	struct intel_guc *guc;
+
+	if (!gt || !ce || !engine)
+		return false;
+
+	guc = &gt->uc.guc;
+	if (!guc->capture)
+		return false;
+
+	/*
+	 * Look for a matching GuC reported error capture node from
+	 * the internal output link-list based on lrca, guc-id and engine
+	 * identification.
+	 */
+	list_for_each_entry(n, &guc->capture->outlist, link) {
+		if (n->eng_inst == GUC_ID_TO_ENGINE_INSTANCE(engine->guc_id) &&
+		    n->eng_class == GUC_ID_TO_ENGINE_CLASS(engine->guc_id) &&
+		    n->guc_id == ce->guc_id.id &&
+		    (n->lrca & CTX_GTT_ADDRESS_MASK) == (ce->lrc.lrca & CTX_GTT_ADDRESS_MASK))
+			return true;
+	}
+
+	return false;
+}
+
 void intel_guc_capture_get_matching_node(struct intel_gt *gt,
 					 struct intel_engine_coredump *ee,
 					 struct intel_context *ce)
@@ -1555,6 +1585,7 @@ void intel_guc_capture_get_matching_node(struct intel_gt *gt,
 		return;
 
 	GEM_BUG_ON(ee->guc_capture_node);
+
 	/*
 	 * Look for a matching GuC reported error capture node from
 	 * the internal output link-list based on lrca, guc-id and engine

drivers/gpu/drm/i915/gt/uc/intel_guc_capture.h

@@ -11,6 +11,7 @@
 struct drm_i915_error_state_buf;
 struct guc_gt_system_info;
 struct intel_engine_coredump;
+struct intel_engine_cs;
 struct intel_context;
 struct intel_gt;
 struct intel_guc;
@@ -20,6 +21,8 @@ int intel_guc_capture_print_engine_node(struct drm_i915_error_state_buf *m,
 					const struct intel_engine_coredump *ee);
 void intel_guc_capture_get_matching_node(struct intel_gt *gt, struct intel_engine_coredump *ee,
 					 struct intel_context *ce);
+bool intel_guc_capture_is_matching_engine(struct intel_gt *gt, struct intel_context *ce,
+					  struct intel_engine_cs *engine);
 void intel_guc_capture_process(struct intel_guc *guc);
 int intel_guc_capture_getlist(struct intel_guc *guc, u32 owner, u32 type, u32 classid,
 			      void **outptr);

drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c

@@ -4728,13 +4728,37 @@ static void capture_error_state(struct intel_guc *guc,
 {
 	struct intel_gt *gt = guc_to_gt(guc);
 	struct drm_i915_private *i915 = gt->i915;
-	struct intel_engine_cs *engine = __context_to_physical_engine(ce);
 	intel_wakeref_t wakeref;
+	intel_engine_mask_t engine_mask;
+
+	if (intel_engine_is_virtual(ce->engine)) {
+		struct intel_engine_cs *e;
+		intel_engine_mask_t tmp, virtual_mask = ce->engine->mask;
+
+		engine_mask = 0;
+		for_each_engine_masked(e, ce->engine->gt, virtual_mask, tmp) {
+			bool match = intel_guc_capture_is_matching_engine(gt, ce, e);
+
+			if (match) {
+				intel_engine_set_hung_context(e, ce);
+				engine_mask |= e->mask;
+				atomic_inc(&i915->gpu_error.reset_engine_count[e->uabi_class]);
+			}
+		}
+
+		if (!engine_mask) {
+			guc_warn(guc, "No matching physical engine capture for virtual engine context 0x%04X / %s",
+				 ce->guc_id.id, ce->engine->name);
+			engine_mask = ~0U;
+		}
+	} else {
+		intel_engine_set_hung_context(ce->engine, ce);
+		engine_mask = ce->engine->mask;
+		atomic_inc(&i915->gpu_error.reset_engine_count[ce->engine->uabi_class]);
+	}
 
-	intel_engine_set_hung_context(engine, ce);
 	with_intel_runtime_pm(&i915->runtime_pm, wakeref)
-		i915_capture_error_state(gt, engine->mask, CORE_DUMP_FLAG_IS_GUC_CAPTURE);
-	atomic_inc(&i915->gpu_error.reset_engine_count[engine->uabi_class]);
+		i915_capture_error_state(gt, engine_mask, CORE_DUMP_FLAG_IS_GUC_CAPTURE);
 }
 
 static void guc_context_replay(struct intel_context *ce)

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -808,10 +808,15 @@ static void err_print_gt_engines(struct drm_i915_error_state_buf *m,
 	for (ee = gt->engine; ee; ee = ee->next) {
 		const struct i915_vma_coredump *vma;
 
-		if (ee->guc_capture_node)
-			intel_guc_capture_print_engine_node(m, ee);
-		else
+		if (gt->uc && gt->uc->guc.is_guc_capture) {
+			if (ee->guc_capture_node)
+				intel_guc_capture_print_engine_node(m, ee);
+			else
+				err_printf(m, "  Missing GuC capture node for %s\n",
+					   ee->engine->name);
+		} else {
 			error_print_engine(m, ee);
+		}
 
 		err_printf(m, "  hung: %u\n", ee->hung);
 		err_printf(m, "  engine reset count: %u\n", ee->reset_count);